Genetics of Neonatal Hyperinsulinism

Arch Dis Child Fetal Neonatal Ed 2000;82:F79–F86 F79 Arch Dis Child Fetal Neonatal Ed: first published as 10.1136/fn.82.2.F79 on 1 March 2000. Downloaded from

HYPERINSULINISM

Genetics of neonatal hyperinsulinism

Benjamin Glaser, Paul Thornton, Timo Otonkoski, Claudine Junien

Abstract Netherlands.2 In areas of high consanguinity, Congenital hyperinsulinism (HI) is a the incidence can be as high as one in 3000.13 clinically and genetically heterogeneous The clinical heterogeneity includes a highly entity. The clinical heterogeneity is mani- variable age of onset, severity, and responsive- fested by severity ranging from extremely ness to medical treatment. The pathological severe, life threatening disease to very findings are also variable, and two distinct his- mild clinical symptoms, which may even topathological forms have been described. be diYcult to identify. Furthermore, clini- Most cases show diVuse involvement of â cells cal responsiveness to medical and surgical throughout the pancreas (diVuse HI), whereas management is extremely variable. Re- some have focal adenomatous hyperplasia cent discoveries have begun to clarify the (focal HI), in which a distinct region of the Department of molecular aetiology of this disease and pancreas appears to be involved, the remainder Endocrinology and thus the mechanisms responsible for this of the pancreas being histologically and func- Metabolism, The clinical heterogeneity are becoming more tionally normal. Genetic heterogeneity has also Hebrew University, been described. Mutations in four diVerent Hadassah Medical clear. Mutations in 4 diVerent genes have School, Jerusalem, been identified in patients with this clini- genes have been detected in patients with HI, http://fn.bmj.com/ 91120, Israel cal syndrome. Most cases are caused by and both autosomal recessive and dominant B Glaser mutations in either of the 2 subunits of the inheritance has been demonstrated. However, + in many cases the genetic aetiology is still not Division of â cell ATP sensitive K channel (KATP), Endocrinology, whereas others are caused by mutations in known. In this review, we will attempt to Department of the â cell enzymes glucokinase and gluta- provide an update for each of the known Paediatrics, University of Pennsylvania School mate dehydrogenase. However, for as subclassifications of HI, while emphasising of Medicine, many as 50% of the cases, no genetic aeti- those areas where research is still needed. on October 1, 2021 by guest. Protected copyright. Philadelphia, PA ology has yet been determined. The study 19104, USA of the genetics of this disease has provided P Thornton Control of insulin secretion important new information about â cell To understand the pathophysiology of the vari- Transplantation physiology. Although the clinical ramifi- ous forms of HI, one must understand the Laboratory, Haartman cations of these findings are still limited, Institute, University of mechanisms responsible for glucose homeosta- Helsinki, Helsinki FIN in some situations genetic studies might sis. Under normal conditions, the circulating 00014, Finland greatly aid in patient management. glucose concentration is regulated, primarily T Otonkoski ( 2000;82:F79–F86) Arch Dis Child Fetal Neonatal Ed by insulin, to within a very tight range. INSERM Unité 383, Keywords: hypoglycaemia; sulphonylurea receptor; Unregulated release of insulin will result in Génétique, hypoglycaemia with resultant neuroglycopenia Chromosome et ATP sensitive potassium channel; hyperinsulinism Cancer, Hopital des and, if uncontrolled, irreversible brain damage. Enfants Malades, The major factors that control glucose 75743 Paris, France Congenital hyperinsulinism (HI) is a heteroge- stimulated insulin secretion are described in fig Claudine Junien neous entity, the genetics of which have only 1. Although this figure gives a highly simplified Correspondence to: recently begun to be elucidated. The incidence description of the regulation of insulin secre- Dr B Glaser, Division of Endocrinology and of HI in the general population ranges from tion and fails to consider multiple other Metabolism, Hadassah one in 27 000 in the Irish population (P pathways that modulate the response to University Hospital, PO Box 12000, Jerusalem, Israel Thornton, unpublished observations) to one in glucose and to other stimuli, it is suYcient for email: [email protected] 40 000 in Finland,1 and one in 50 000 in the the purpose of the discussion here. F80 Glaser, Thornton, Otonkoski, Junien Arch Dis Child Fetal Neonatal Ed: first published as 10.1136/fn.82.2.F79 on 1 March 2000. Downloaded from

The normal, resting â cell membrane is tion and unregulated insulin secretion. In most maintained in a hyperpolarised state by the cases, insulin secretion will not respond to dia- Na+–K+ ATPase pump and open, ATP sensitive zoxide or to tolbutamide because a functional

potassium channels (KATP). These channels channel is required for these drugs to exert sense the metabolic state of the cell. When their eVect. However, some KATP mutations plasma glucose increases, it enters the â cell might cause lack of function in the natural through a specific membrane-bound glucose state, yet retain the ability to respond to phar- transporter—GLUT-2. It is then phosphor- macological intervention. ylated by the enzyme glucokinase and metabo- In contrast, mutations that increase nutrient lised, resulting ultimately in the phosphoryla- metabolism and thus increase the ATP/ADP tion of ADP to ATP, thereby increasing the ratio will result in insulin secretion that is sup- pressible with diazoxide. As described below, ATP/ADP ratio. This causes the KATP channels to close, which results in depolarisation of the mutations at both of these sites have been cell membrane, opening of voltage dependent found in patients with HI. Theoretically, muta- Ca2+ channels, and a rise in the free intracellu- tions in genes responsible for functions down- 2+ lar Ca concentration. This, in turn, activates stream from the KATP channel, such as the volt- 2+ the insulin secretory mechanisms. Glucokinase age gated Ca channels or genes involved in is the rate limiting step in the metabolism of the mobilisation of secretory granules, could glucose and is thus a key step in the regulation also cause unregulated insulin secretion, al- of the secretion of insulin. The ATP/ADP ratio though no such mutations have yet been iden- can be increased by metabolism of substrates tified. other than glucose, such as amino acids. Activating mutations of glutamate dehydroge- Mutations in the â cell KATP channel nase (GDH) cause unregulated insulin secre- The first evidence that HI is a genetic disease came with the identification of rare families tion, possibly by increasing the flux of sub- 6–14 strates into the citric acid cycle, thus increasing with aVected siblings. More concrete evi- the ATP/ADP ratio. dence for autosomal recessive inheritance came from statistical analysis of relatively large The KATP channel can be regulated by drugs, 15 16 the most common of which are the antidiabetic groups of patients and their families. Link- age studies carried out in a subgroup of sulfonylureas (tolbutamide, glibenclamide, gli- families selected specifically for evidence of pizide, and others), which cause closure of the recessive inheritance (at least two aVected sib- channel, membrane depolarisation, and insulin lings with unaVected parents) showed linkage secretion. Diazoxide has the opposite eVect, to chromosome 11p15.1, which was subse- increasing the channel’s mean open probabil- quently confirmed.17 18 ity, thus inhibiting insulin secretion, and is Soon after the linkage was established, the â commonly used in states of unregulated insulin cell sulfonylurea receptor gene (SUR1) was secretion, particularly insulinomas and some cloned.19 The gene was located within the cru- cases of HI. A natural ligand for the K chan- ATP cial region for the HI gene, as defined by link- nel has been described recently (endosul- age analysis, and mutations were identified in phine), but its physiological role in the regula- 20 45 nine families with HI. Thus, the first HI asso- tion of insulin secretion is still unknown. ciated gene was discovered. Soon thereafter, Mutations in several diVerent genes might be +

the gene encoding the inward rectifying K http://fn.bmj.com/ predicted to cause a similar phenotype: inap- channel (KIR6.2) was cloned and it was propriate insulin secretion and hypoglycaemia. discovered that together with SUR1 the Mutations that decrease or destroy KATP chan- product of this gene formed the â cell KATP nel activity will result in continuous depolarisa- 21 channel. Dunne et al proved the association between SUR1 mutations, K channel func- + ATP K tion, and HI by demonstrating a lack of K Sulfonylureas Ca++ ATP

SUR-1 channel function in â cells obtained at the time on October 1, 2021 by guest. Protected copyright. of pancreatectomy from a patient known to be Diazoxide homozygous for an SUR1 mutation.22 The Depolarisation KIR6.2 gene is located adjacent to the SUR1 Kir 6.2 gene on chromosome 11p and, based on the ATP/ADP linkage data, it too is a candidate gene for HI ratio 23 Ca++ associated mutations. 24–26 α ketoglutarate To date, three KIR6.2 mutations and K+ Glucose-6-P + NH3 more than 40 SUR1 mutations have been reported.1 20 26–30 SUR1 mutations are spread Glucokinase GDH throughout the coding region of the gene (ﬁg GLUT-2 Glucose 2), although there is an apparent clustering of Glucose Glutamate mutations in the second nucleotide binding Insulin domain. In vitro studies of how these mutations aVect channel function are providing Figure 1 The major pathways responsible for glucose regulation of insulin secretion are important new information about how this shown. Hyperinsulinism (HI) can be caused by mutations in the genes encoding the four protein regulates channel function.31–33 Some proteins highlighted with boxes. The ATP sensitive potassium channel (KATP) is composed of four molecules of SUR1 and four of Kir 6.2, as shown schematically. Glucokinase is the rate mutations completely eliminate channel activ- limiting step in the metabolism of glucose and thus regulates changes in the intracellular ity, whereas others alter channel density or ATP/ADP ratio in response to extracellular glucose concentrations. The mechanism by which activating mutations in the glutamate dehydrogenase (GDH) gene cause unregulated channel activity in response to intracellular insulin secretion has not yet been conﬁrmed experimentally. nucleotide concentrations. A lack of response Genetics of hyperinsulinism F81 Arch Dis Child Fetal Neonatal Ed: first published as 10.1136/fn.82.2.F79 on 1 March 2000. Downloaded from

R74Q6 Del 4138CGAC8 5 5 5 4144 (complex) A116P W1338X 6 6 5 G1379R H125Q R1352P 6 5 G1382S 6 V1360M 5 5 S1387F 2 N188S6 L508P Q954X 6 G1479R 5 R1394H 5 V187D7 S957F R1494W 6 6 6 5 5 F591L K890T5 T1139M R1421C E1507K N406D 3 7 5 G716V 5 6 A1457T C418R R836X R1215Q 5 5 R620C5 L1544P R248X R842G8

110 20 301508 insAS6 3 1 679 ins 18 nt5 2291 –1g to a 4310 g to a 5 6 Nt 731 del a 2117 –1 g to a 4 5 delF1388 L226 ins 5 aa 1885 delc5 1893delt(ter)6 3992 –3 c to g6 6 1 949delc(ter) 1671 –20 a to g3 3992 –9 g to a 5 1260 ins 31 1630 +1 g to t6 Figure 2 Schematic of the SUR1 gene showing 39 exons (rectangles) and introns (lines connecting the exons). Neither is drawn to scale. The two nucleotide binding domains are shaded in grey. Mutations published to date are shown. Missense and nonsense mutations are shown above the gene, whereas intronic mutations, insertions, and deletions are depicted below the gene. Superscripts indicate references in which the speciﬁc mutations are described: 1, Thomas and colleagues20;2, Nichols and colleagues31; 3, Thomas and colleagues27; 4, Nestorowicz and colleagues28; 5, Aquilar-Bryan and Bryan26;6, Nestorowicz and colleagues29; 7, Otonkoski and colleagues1; and De Lonlay-Debeney et al.30

to increased MgADP concentrations appears each case there is a diVerent mutation (P to be a defect common to several diVerent Thornton and B Glaser, unpublished data, mutations.31 32 All reported SUR1 and KIR6.2 1999). mutations appear to be recessive, because het- Interestingly, in over half of the patients erozygous parents and siblings are clinically screened for mutations in the entire SUR1 and KIR6.2 coding regions, no mutation was iden- normal. However, because the functioning KATP channel is a hetero-octomer composed of four tified. To date, no systematic search of the pro- molecules of SUR1 and four molecules of moter regions of these genes has been reported, KIR6.2,34 and because a dominant negative although such studies are currently in progress. KIR6.2 mutation has been engineered into the mouse homologue of this gene,35 it is possible Mutations in the glutamate that dominant mutations occur in humans. dehydrogenase gene Most of the mutations are extremely rare, Recently, patients were described with HI and and most were found to be unique to specific apparently asymptomatic hyperammonaemia. families. However, some exceptions exist. In No known defects of ammonia metabolism 36 37 the Ashkenazi Jewish population, at least 88% were identified. Increased glutamate dehy- http://fn.bmj.com/ of the disease associated chromosomes carry drogenase (GDH) activity was found in one of two specific mutations.28 More recently, peripheral lymphocytes from these patients, a founder mutation (V187D) was found in and genomic mutations in the regulatory domain of the enzyme were identified.38 To Finnish patients with HI. Eighteen of 42 date, six mutations in this gene (GLUD-1) disease associated chromosomes from Finnish have been described in patients with the hyper- patients carried this mutation.1 In contrast, out

insulinism hyperammonaemia syndrome. All on October 1, 2021 by guest. Protected copyright. of a group of 16 Irish patients, mutations have are located in the allosteric regulatory domain been identified in only three probands, and in of the enzyme, and all are dominant mutations (fig 3). Some families with multigeneration Catalytic Allosteric domain domain dominant inheritance have been identified, whereas the other mutations were identified as de novo mutations in aVected probands. One particular mutation (S445L) appears to repre- 12345678910 11 12 13 sent a mutation hot spot because it has been found to occur de novo in three independent cases. GDH catalyses the reversible reaction EXON 11 EXON 12 converting glutamate to á-ketoglutarate, a substrate for the citric acid cycle in the â cell (fig 1). The precise mechanism by which these S445L Q494R mutations cause the hyperinsulinism hyperam- H454Y monaemia syndrome has not been confirmed; G446S however, the known function of this enzyme G446D S448P has led to a plausible hypothesis, although this has yet to be tested experimentally.38 Increased Figure 3 Schematic diagram of the glutamate dehydrogenase gene (GLUD1) showing the exons as rectangles and the introns as lines connecting the exons. The locations of the six enzyme activity might result in increased flux published mutations in exons 11 and 12 are shown.38 of amino acid substrates through F82 Glaser, Thornton, Otonkoski, Junien Arch Dis Child Fetal Neonatal Ed: first published as 10.1136/fn.82.2.F79 on 1 March 2000. Downloaded from

á-ketoglutarate into the citric acid cycle, lular sensor of glucose concentrations. Indeed, resulting in increased conversion of ADP to mutations in glucokinase that decrease enzy-

ATP, closure of the KATP channel, membrane matic activity cause one form of autosomal depolarisation, and finally insulin secretion. dominant type 2 diabetes (maturity onset This increased secretion will occur without any diabetes of the young). Genomic DNA from correlation with glucose concentrations, but is the proband of this family was screened for triggered by high protein diets, which increase mutations in the glucokinase gene (GK) and a the amino acid substrate availability and there- missense mutation (V455M) in exon 10 was fore increase insulin secretion. Indeed, these identified. Linkage analysis confirmed that the patients exhibit a pronounced worsening of mutation co-segregated with clinical disease, their hypoglycaemia after high protein intake and in vitro studies of the mutant enzyme and have prolonged, severe hypoglycaemia revealed a considerably increased aYnity for after an oral leucine load. Thus, many of these glucose. This defect readily explains the clinical patients would have been described in the early phenotype in these patients. As expected, these HI literature as having leucine sensitive hypo- patients respond well to diazoxide treatment. glycaemia. In the liver, increased activity of this We did not find this mutation in any other enzyme also results in increased glutamate to proband with HI, and neither did we find any á-ketoglutarate conversion, thus increasing GK mutation in any of the other six families ammonia production and decreasing glutamate with apparent autosomal dominant inherit- concentrations. Glutamate is an essential ance. In a separate cohort of 30 infants with substrate for the formation of N-acetyl gluta- hyperinsulinism, systematic screening of the mate (NAG), an allosteric stimulator of entire coding sequence failed to identify any carbamoyl phosphate synthetase. Decreased GK mutations (C Bellané-Chantelot, unpub- concentrations of NAG cause decreased car- lished data, 1999). Thus, we conclude that this bamoyl phosphate synthetase activity and form of HI is probably exceedingly rare. accumulation of ammonia by inhibition of the urea cycle. Treatment with diazoxide is eVec- Phenotype–genotype correlations tive in most patients, consistent with the The clinical phenotypes associated with GDH hypothesis that the defect is proximal to the and GK mutations are described above, and for

KATP channel. Recently, however, two unrelated these mutations, the phenotypes and genotypes patients with hyperinsulinism hyperammonae- appear to correlate quite well. In contrast, mia syndrome were described who have muta- when trying to correlate the clinical phenotype tions in the allosteric domain of GDH and are with specific SUR1 mutations, the situation is unresponsive to diazoxide treatment (P Delon- quite diVerent. All mutations identified to date lay et al, unpublished data). This suggests that are recessive, and most are rare. Therefore, the mechanism by which GDH mutations most patients with HI are compound heterozy- cause hyperinsulinism might be diVerent from gotes for HI mutations, or only a single muta- that presented above. The hyperinsulinism tion is identified. In either case, correlations hyperammonaemia syndrome appears to be a between the clinical disease and the in vitro rare cause of hyperinsulinaemic hypoglycaemia function of the mutant channel is diYcult or because only five of 170 probands with HI in impossible. However, some patients are homo- our series were found to have mutations in this zygous for specific mutations, usually because

gene (B Glaser, unpublished data, 1998). the patients come from a genetically isolated http://fn.bmj.com/ Eleven other patients with hyperammonaemia population, or because of consanguinity. are currently being investigated; three were Mutations “SUR1 949 del c” and “KIR6.2 resistant to diazoxide. So far, in ﬁve, no muta- T12X” result in termination codons (the tions have been found in the allosteric domain former by means of a frameshift) early in the (C Junien, unpublished data, 1999). coding sequence of SUR1 and KIR6.2, respectively. Individuals homozygous for each of

Glucokinase mutations these mutations have been identiﬁed and all on October 1, 2021 by guest. Protected copyright. A family with a unique form of HI with ﬁve have clinically very severe disease that is unre- aVected individuals in three generations was sponsive to diazoxide or somatostatin ana- described recently.39 Two patients had detailed logue. The latter drug has been used eVectively evaluation of the control of insulin secretion in some patients with HI,41 and appears to work

that revealed qualitatively normal control, with by inhibiting both KATP channel closure and good insulin responses to both intravenous and insulin secretion at more distal sites in the oral glucose load, and suppression of insulin insulin secretory cascade. Interestingly, these secretion during insulin induced hypoglycae- mutations do not appear to be associated with mia. However, fasting and postprandial glucose any defects in other organ systems, suggesting concentrations were low, below the threshold the neither of these two proteins are crucial for of symptomatic neuroglycopenia. The data the normal function of other tissues or suggested a defect in the glucose threshold at organs.25 29 which insulin secretion is turned oV. In normal Mutation “SUR1 4310 g→a” results in individuals, insulin secretion is completely abnormal exon splicing and the complete inhibited at about 4 mmol/litre glucose.40 In removal of the second nucleotide binding these patients, however, apparent inhibition of domain of SUR1.20 â Cells isolated from a insulin secretion occurred at 2 mmol/litre, patient homozygous for this mutation failed to 22 resulting in both fasting and reactive hypogly- show any KATP channel activity. The resultant caemia. Glucokinase is the rate limiting step in phenotype was, as expected, very severe the metabolism of glucose, and acts as the cel- disease, unresponsive to diazoxide treatment. Genetics of hyperinsulinism F83 Arch Dis Child Fetal Neonatal Ed: first published as 10.1136/fn.82.2.F79 on 1 March 2000. Downloaded from

Two other mutations have been described in the pathophysiology of the entity was not homozygous patients. The delF1388 mutation known until very recently. de Lonlay et al is found in approximately 20% of the reported loss of maternal chromosome 11p in Ashkenazi Jewish HI associated chromosomes, the focal lesions of 10 probands with HI.45 A but only two patients homozygous for the similar ﬁnding was previously reported in one mutation have been described. As expected adult patient with insulinoma.46 The chromo- from the in vitro studies that show no channel some loss apparently occurs during develop- activity if this mutation is present, both patients ment of the pancreas, and aVects only â cells in had very severe disease. Both were treated with one speciﬁc region of the gland. The precise somatostatin analogue along with frequent timing and location of the somatic event deter- feeding and night time continuous intragastric mines the location and extent of the aVected feedings, and neither underwent surgery. The region. The chromosome deletion contains at V187D mutation has been reported in 15 of 24 least two imprinted, maternally expressed cases from central Finland. Six of the patients genes (p57KIP2 and H19) that encode important were homozygous and nine heterozygous for cell cycle regulators, and an imprinted, pater- the mutation. Interestingly, all of these patients nally expressed gene encoding a growth were equally severely aVected. This mutation stimulator—insulin like growth factor 2

eliminates KATP channel function and, as (IGF2). Thus, in â cells with the maternal expected, results in a very severe, drug allele deleted, the growth suppressing genes are unresponsive phenotype.1 not expressed, whereas the growth stimulating The splice site mutation (3992 –9 g→a), gene is normally expressed, a combination that found in approximately 70% of Ashkenazi Jew- results in abnormal proliferation of aVected â ish HI associated chromosomes, is of particular cells. However, these patients have very severe, interest. Most patients homozygous for this diazoxide unresponsive HI, and thus, abnormal mutation have severe disease that responds â cell proliferation alone is not suYcient to poorly to treatment with diazoxide. However, explain the clinical phenotype. In all patients we have identified two families with multiple reported by de Lonlay et al, the SUR1 and siblings in which the proband was homozygous KIR6.2 loci were within the region deleted; for this mutation and had severe HI, whereas however, there is no evidence to suggest that three siblings, who were also homozygous for either of these two genes is imprinted, so alter- the same mutation, had very mild disease or native explanations were needed. were clinically unaVected (H Landau, personal Recently, Ryan et al and Verkarre et al communication, 1997). These are both described five patients with focal HI, loss of the Ashkenazi families in which this is a founder maternal chromosome 11p in the lesion, and a mutation.42 Therefore, the severe and the mild heterozygous germline mutation on the pater- cases were all genetically identical at this locus, nal SUR1 allele.47 48 Another seven patients a finding that was confirmed by haplotype with focal HI, all presenting with a paternally analysis. This observation suggests that some inherited germline mutation, have been subse- splice mutations might be variably expressed quently identified (JC Fournet et al, unpub- and that, with diVerent genetic backgrounds, a lished data, 1999).49 Somatic loss of the mater- diVerent percentage of normal protein might nal allele of chromosome 11p in a patient be produced. A similar phenomenon has been carrying a SUR1 mutation on the paternal

found in patients with a splice site mutation in allele results in reduction to hemizygosity or http://fn.bmj.com/ the gene encoding 17 hydroxylase.43 Most homozygosity for the mutant allele in the patients homozygous for this mutation have aVected â cells. Therefore, the â cells within severe congenital adrenal hyperplasia; however, the focal lesion will proliferate, presumably asymptomatic homozygous patients with ap- because of unbalanced production of tumour parent near normal enzyme function have been growth suppressing and growth stimulating

identiﬁed. factors, and will lack functional KATP channels.

Occasionally, the genotype and phenotype This will cause unregulated insulin secretion on October 1, 2021 by guest. Protected copyright. can be correlated with electrophysiological that is unresponsive to drug treatment. There- properties of â cells obtained from pancreatec- fore, the combination of a paternally inherited tomy specimens. Although in some cases the SUR1 mutation, along with a second somatic correlation is excellent,122in others clinical and event causing the loss of chromosome 11p will in vitro findings do not correlate (P Thornton create a proliferating â cell population that and M Dunne, unpublished data, 1999). This secretes insulin in an unregulated manner, thus might be because of the diYculty in diVerenti- completely explaining the clinical phenotype of ating cases of focal disease (see below) from focal HI. diVuse disease using the current techniques of It is not possible to study the natural history â cell isolation. of focal HI directly because the definitive diagnosis of focal disease can only be made at the HI as a result of focal lesions time of surgical resection. However, a cohort of Ever since HI was initially described, there has medically treated patients was recently re- been controversy about the histopathological ported who are heterozygous for SUR1 muta- findings associated with the clinical syndrome. tions on the paternal chromosome. The unique One of the major controversies related to the genetic characteristics of this cohort suggested existence of a group of patients in whom only a that most of the patients have focal disease. part of the pancreas is aVected—so called focal Interestingly, these patients appear to enter HI.11 44 Although careful histological examina- clinical remission after a mean of about 16 tion did demonstrate focal HI in some cases, months of medical treatment. A review of F84 Glaser, Thornton, Otonkoski, Junien Arch Dis Child Fetal Neonatal Ed: first published as 10.1136/fn.82.2.F79 on 1 March 2000. Downloaded from

histology from three other patients with Clinical ramifications of genetic findings confirmed focal lesions showed increased â cell HI is a genetically heterogeneous entity. apoptosis within the focal lesion. It was During the past three years major advances hypothesised that, if treated medically, focal have been made in our understanding of the lesions will undergo apoptosis and disappear, molecular genetic aetiology of this syndrome. leaving the patient with normal â cell Although these discoveries have provided function.49 important new information about â cell physi- The importance of these findings is clear, but ology, the clinical usefulness of these findings is how they should be incorporated into the clini- still limited. However, in some situations, the cal decision making process is less clear. In dif- recent discoveries have already been translated fuse HI, all â cells are abnormal. Therefore, into clinically useful tests providing rapid clini- partial pancreatectomy invariably leads to per- cal diagnosis and providing the basis for more sistent hypoglycaemia or early diabetes, de- precise genetic counselling. Hyperinsulinsim with hyperammonaemia is pending on the extent of the resection. Most, if a new syndrome, the genetics of which are now not all, of these patients will eventually develop known. Previously, the finding of hypoglycae- insulin requiring diabetes during childhood or mia and raised concentrations of ammonia adolescence.50 In sharp contrast, in patients suggested a disorder of fatty acid oxidation. In with focal HI, the remaining pancreas is func- light of these discoveries, the diVerential tionally normal. Therefore, selective excision of 30 diagnosis of patients with neonatal or infantile the focal region results in complete cure. hypoglycaemia should be extended to include However, if patients with focal HI do enter the hyperinsulinsm and hyperammonaemia complete remission after medical treatment, as syndrome. If raised or borderline ammonia suggested by the above cited study, then concentrations are found, rapid genetic diag- perhaps surgery can be avoided, because even nosis is now possible in most cases. In contrast under the best circumstances, pancreatic sur- to most patients with HI, children with GDH gery carries with it a certain morbidity and mutations usually respond to diazoxide treat- mortality. ment, and in most surgery can be avoided. In In the absence of long term follow up data on many, the disease is caused by a de novo muta- medically treated patients with confirmed focal tion, suggesting that the chances that a lesions, it seems logical to decide whether or subsequent sibling will be aVected are ex- not to operate on a particular patient with focal tremely small. In other families, autosomal HI based on the degree of diYculty encoun- dominant inheritance can be documented, tered when attempting medical treatment. meaning that future siblings have a 50% This, however requires a preoperative diagnosis chance of being aVected. of focal HI, and this has proved to be very dif- The clinical usefulness of genetic evaluation ficult. Trans-hepatic portal venous sampling of in patients with HI without hyperammonaemia insulin concentrations during induced, con- is more complicated. In as many as 50% of trolled hypoglycaemia has been used exten- these patients, no mutation may be found in sively and appears to be a reliable, albeit a the coding regions of SUR1 and KIR6.2. The technically very diYcult, procedure that is not genetic diagnosis in these cases is still totally available in most centres.51 Recently, it was unknown. Even in patients with SUR1 or

proposed that the insulin response to intra- KIR6.2 mutations, in most populations no http://fn.bmj.com/ venous tolbutamide could be used to diVeren- founder mutation has been described. Because tiate diVuse from focal disease. The test is the gene is very large (39 exons), screening of based on the hypothesis that patients with focal the entire coding sequence using conventional HI will have a considerable â cell mass that has techniques is not feasible in the clinical setting. In sharp contrast, in populations in which a normal KATP channels and therefore will respond to tolbutamide, whereas in patients founder mutation is known, genetic analysis

can provide very important clinical infor- on October 1, 2021 by guest. Protected copyright. with diVuse HI, the entire â cell mass is mation. In the Ashkenazi Jewish population, we aVected and, hence, no response to tolbuta- routinely use mutation analysis to aid the clini- mide will be seen. Although preliminary data cal diagnosis. Frequently, a genetic diagnosis suggest that this may in fact be a clinically use- can be made even before results on hormone ful test (CA Stanley and A Grimberg, personal analysis are obtained. Furthermore, genetic communication), many more patients need to analysis is now used routinely for genetic be tested at the time of diagnosis, before this counselling in this population. test can be recommended for clinical use. Par- Because of the unique clinical characteristics ticularly worrying is the fact that for about 50% of focal HI described above, and because mod- of patients the molecular diagnosis is not ern, non-invasive imaging techniques are not known, and therefore the response to tolbuta- useful in diagnosing this entity, rapid genetic mide cannot be predicted. Some patients with diagnosis would be very valuable clinically. insulinomas respond to tolbutamide with a Unfortunately, because of the large number of massive output of insulin and severe, prolonged possible mutations in the SUR1 gene, this is hypoglycaemia. It is not known whether some not yet possible in most populations. In popu- forms of HI will respond similarly. Despite lations with founder mutations, genetic analy- these diYculties, the search for an eVective test sis can provide evidence for, but not deﬁnitive is worthwhile, because the ability to diagnose proof of, the presence of this entity. For exam- focal HI preoperatively could radically change ple, in Ashkenazi patients, if two mutant alleles the clinical approach to patients with HI. are identiﬁed, or if a single mutation is Genetics of hyperinsulinism F85 Arch Dis Child Fetal Neonatal Ed: first published as 10.1136/fn.82.2.F79 on 1 March 2000. Downloaded from

identified on the maternal allele, focal HI can form of persistent hyperinsulinemic hypoglycemia of infancy in Finland. Diabetes 1999;48:408–15. be excluded. In the latter case, the presence of 2 Bruining GJ. Recent advances in hyperinsulinism and the a novel, unidentified mutation on the paternal pathogenesis of diabetes mellitus. Curr Opin Pediatr 1990;2:758–65. allele is postulated. If a single mutation is iden- 3 Mathew PM, Young JM, Abu OY, et al. Persistent neonatal tified on the paternal allele, then focal HI is hyperinsulinism. Clin Pediatr (Phila) 1988;27:148–51. 4 Virsolvy-Vergine A, Salazar G, Sillard R, Denoroy L, Mutt suggested; however, given current technology, V, Bataille D. Endosulfine, endogenous ligand for the the presence of another, novel mutation on the sulphonylurea receptor: isolation from porcine brain and partial structural determination of the alpha form. maternal allele cannot be entirely excluded. It Diabetologia 1996;39:135–41. is in this instance that studies of the acute insu- 5 Heron L, Virsolvy A, Peyrollier K, et al. Human alpha- endosulfine, a possible regulator of sulfonylurea-sensitive lin response to diVerent stimuli might be the KATP channel: molecular cloning, expression and biologi- key to preoperative diagnosis and might alter cal properties. Proc Natl Acad Sci U S A 1998;95:8387–91. 6 Woo D, Scopes JW, Polak JM. Idiopathic hypoglycaemia in the management of the patients (see discussion sibs with morphological evidence of nesidioblastosis of the above). pancreas. Arch Dis Child 1976;51:528–31. 7 Moreno LA, Turck D, Gottrand F, Fabre M, Manouvrier HS, Farriaux JP. Familial hyperinsulinism with nesidiob- Nomenclature lastosis of the pancreas: further evidence for autosomal recessive inheritance. Am J Med Genet 1989;34:584–6. Since its initial description, the clinical syn- 8 Woolf DA, Leonard JV, Trembath RC, Pembrey ME, Grant drome of hyperinsulinaemic hypoglycaemia of DB. Nesidioblastosis: evidence for autosomal recessive inheritance. Arch Dis Child 1991;66:529–30. infancy has been referred to by a large number 9 Becker K, Wendel U, Przyrembel H, Tsotsalas M, of diVerent descriptive names. Now that the Müntefering H, Bremer HJ. Beta cell nesidioblastosis. Eur J Pediatr 1978;127:75–89. aetiology of the disease is becoming known, we 10 Schwartz SS, Rich BH, Lucky AW, et al. Familial nesidiob- believe that it is time to standardise the lastosis: severe neonatal hypoglycemia in two families. Pediatrics 1979;95:44–53. nomenclature used to describe the syndrome. 11 Rahier J, Falt K, Muntefering H, Becker K, Gepts W, Falk- We suggest using the term “hyperinsulinism mer S. The basic structural lesion of persistent neonatal hypoglycaemia with hyperinsulinism: deficiency of pancre- (HI)” as a general term. When other clinical or atic D cells or hyperactivity of B cells? Diabetologia histological characteristics are known these 1984;26:282–9. 12 Horev Z, Ipp M, Levey P, Daneman D. Familial hyperin- should be stated, such as HI/HA for the hyper- sulinism: successful conservative management. J Pediatr insulinaemia hyperammonaemia syndrome 1991;119:717–20. 13 Falkmer S, Sovik O, Vidnes J. Immunohistochemical, and focal HI for focal disease. If the genetic morphometric, and clinical studies of the pancreatic islets aetiology is known, then the mutated gene can in infants with persistent neonatal hypoglycemia of familial type with hyperinsulinism and nesidioblastosis. Acta be added to the name, such as HI-SUR1, Biologica et Medica Germanica 1981;40:39–54. HI-KIR6.2, HI-GK, or HI-GLUD1 for pa- 14 Hammersen G, Trefz FR, Schmidt H. Familial nesidioblastosis. J Pediatr 1980;96:778. tients with confirmed mutations in the sub- 15 Glaser B, Phillip M, Carmi R, Lieberman E, Landau H. units of the â cell KATP channel, GK, or GDH Persistent hyperinsulinemic hypoglycemia of infancy (“nesidioblastosis”): autosomal recessive inheritance in 7 genes, respectively. Using this nomenclature it pedigrees. Am J Med Genet 1990;37:511–15. will become easier to identify the precise clini- 16 Thornton PS, Sumner AE, Ruchelli ED, Spielman RS, Baker L, Stanley CA. Familial and sporadic hyperinsulin- cal, biochemical, and physiological characteris- ism: histopathologic findings and segregation analysis sup- tics of each specific disease. Comparison of port a single autosomal recessive disorder. J Pediatr clinical and other data from diVerent centres 1991;119:721–4. 17 Glaser B, Chiu KC, Anker R, et al. Familial hyperinsulinism will be made easier. Furthermore, this ap- maps to chromosome 11p14–15.1, 30 cM centromeric to the insulin gene. Nat Genet 1994;7:185–8. proach might facilitate the identification of 18 Thomas PM, Cote GJ, Hallman DM, Mathew PM. subgroups of patients with novel forms of this Homozygosity mapping, to chromosome 11p, of the gene syndrome for familial persistent hyperinsulinemic hypoglycemia of infancy. Am J Hum Genet 1995;56:416–21.

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